A. Field of the Invention
The present invention relates to a method for producing a steel stock suitable for electric-welded steel tubular products having a superior resistance to sour gas environments where a gas such as H.sub.2 S prevails, and more particularly, to a method for producing the steel stock which is suitable for electric-welded steel tubular products as hot-rolled with no heat treatment.
B. Description of the Prior Art
Since the oil crisis, oil wells have become so deep that the possibility of the oil containing a lot of hydrogen sulfide gas is now very high. In fact, crude oil containing much H.sub.2 S gas is actually being pumped up for processing. Accordingly, line pipe having a strong resistance to H.sub.2 S has come into strong demand and electric-welded steel tubular products having superior resistance to sour gas containing H.sub.2 S are also now required by many users.
It is understood that throughout the specification the term "sour gas" refers to gas containing H.sub.2 S and other S-containing gases. On the other hand, increased oil prices have made it profitable to pump oil from wells containing considerable quantities of H.sub.2 S (having pH as high as 4.0). In consequence, a line pipe having a strong resistance to pH 4.0 has been strongly desired.
There is already in use a line pipe coated with Cu that is able to prevent the penetration of hydrogen in an ordinary environmental situation where the pH is 5.2. A Cu coated line pipe is, however, unable to prevent the invasion of hydrogen in an environment of pH 4.0. Therefore, it is necessary to increase resistance to sour gas by some other means. In this connection, it is known that sour gas resistance can be enhanced by subjecting an electric-welded tube to quenching and tempering. This, however, leads to another disadvantage, namely, a rise in processing cost.